1. Field of the Invention
The present invention relates to a head-rest vertical adjustment device for adjusting the height of a head-rest for a vehicle seat, and, more particularly, to an improved lock mechanism wherein a stopper for locking is integrally formed with a spring material member to bias the stopper in a direction toward engagement grooves formed in head-rest stays.
2. Description of the Prior Art
Conventionally, as one of integral combinations of a stopper and a spring member, there is known a lock mechanism using a lock spring which is formed of such a wire material as disclosed in Japanese Utility Model Publication No. 73448 of 1981. Such conventional lock mechanism is simple in construction since the lock spring is provided at its front end with an integral operation portion such as an operation knob to release a locked condition established by such lock spring. Such conventional lock mechanism, however, presents a disadvantage. Namely, during long periods of use, since forces applied to the operation knob are directly given to the lock spring, the lock spring is caused to deform and thus it will not be able to provide a complete locking.